1. Field of the Invention
The present invention relates to a shake correcting device incorporated in cameras or video cameras, a shake correcting method for apparatuses, such as cameras or video cameras, and a control program for implementing the shake correcting method.
2. Description of the Related Art
Conventionally, an optical shake correcting device has been proposed as a shake correcting device incorporated in image pickup apparatuses, such as cameras or video cameras. The optical shake correcting device performs shake correction by moving at least one of taking lenses in a direction perpendicular to the optical axis thereof and thereby changing the optical axis. FIG. 9 shows an example of the arrangement of the optical shake correcting device (disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2000-66260).
In FIG. 9, reference numeral 101 designates an angular velocity sensor that is comprised of a vibration gyro, and detects a shake of an image pickup apparatus, 102 a bypass filter that eliminates a drift and other undesired components of the output from the angular velocity sensor 101, 103 an amplifier that amplifies an angular velocity signal indicative of the detected angular velocity, and 120 a microcomputer that controls the overall operation of the image pickup apparatus, including autofocus (AF) control, zoom control, automatic exposure (AE) control, mechanical part control, and power supply control.
Reference numeral 104 designates an A/D converter incorporated in the microcomputer 120. The angular velocity signal is converted to a digital signal by the A/D converter 104 to provide angular velocity data. The angular velocity data is subjected to predetermined signal processing through a high-pass filter (HPF) 105 and a phase compensation filter 106, and an integrator 108 at the next stage generates a shake correction signal. The output from the integrator 108 is used as a target drive value for a shift lens 119, and converted into a PWM signal by a pulse width modulator (PWM) 117, followed by being outputted as a PWM output from the microcomputer 120.
Reference numeral 901 designates a low-pass filter (LPF) that converts the PWM output into a direct current corresponding to a correction amount, i.e. the target drive value. Reference numeral 114 designates a position sensor that detects the current position of the shift lens 119, and 905 an amplifier that amplifies the output from the position sensor 114. An adder 902 calculates the difference between the target drive value, i.e. the output from the LPF 901 and a value corresponding to the current position of the shift lens 119, i.e. the amplified output from the position sensor 114. The output from the adder 902 is supplied to a driver 904 that is implemented by an operational amplifier, and the driver 904 passes an electric current through a coil (not shown) that drives the shift lens 119, to thereby move the shift lens 119 such that a desired optical axis correction angle can be obtained. Shake correction is achieved through these operations.
Further, in FIG. 9, symbol Vp designates a power supply for driving the shift lens 119. The electric power of the power supply Vp is supplied to the driver 904. On the other hand, symbol Vc designates a control power supply, and the electric power of the control power supply Vc is used for driving component parts other than the driver 904. Reference numerals 804 and 805 designate switches operated for supplying power from the respective power supplies Vp and Vc to their associated component parts. For example, in a reproduction mode in which the video camera as the image pickup apparatus does not need an anti-shake function, the switches 804 and 805 are kept off by a power supply controller 803 that operates according to commands from the microcomputer 120, whereby the drive current is interrupted for saving energy.
Now, there are problems in turning on and off the power of the shake correcting device. More specifically, if the drive current suddenly starts flowing upon turning-on of the power, a lens retainer frame that retains the shift lens 119 hits against an inner end of a lens barrel, thereby causing large impact noise. On the other hand, when the power is turned off, the retaining force is cancelled and the shift lens 119 drops due to its own weight so that the lens retainer frame hits against an opposite inner end of the lens barrel, thereby also generating impact noise. The impact noise thus generated degrades the quality of the image pickup apparatus.
To overcome the problem that occurs when the power is turned on, the proposed shake correcting device is configured such that a DC potential to be obtained by smoothing the PWM output from the microcomputer 120 becomes equal to the reference voltage of each of the sections or component parts of the device, and the switches 804 and 805 are controlled to be turned on in the same timing, to thereby suppress generation of impact noise due to hitting of the lens retainer frame against the inner end of the lens barrel. On the other hand, to overcome the problem that occurs when the power is turned off, just before the switches 804 and 805 are turned off, the shift lens 119 is caused to slowly move to a point close to the inner end of the lens barrel, and then the switches 804 and 805 are turned off to thereby suppress generation of impact noise to the minimum, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2000-66260.
In the conventional correcting device constructed as above, however, since the shift lens 119 is driven by a drive coil which is driven by the operational amplifier, the circuit has a large internal loss, leading to increased power consumption.
To overcome this inconvenience of increased power consumption, a control method has been proposed e.g. in Japanese Laid-Open Patent Publications (Kokai) No. H08-136962 and No. H11-308521, in which an H bridge circuit is used to drive the drive coil directly by the PWM output.
FIG. 10 is a block diagram showing the arrangement of a conventional optical shake correcting device based on the PWM drive control method using a H bridge circuit. In FIG. 10, component parts and elements corresponding to those shown in FIG. 9 are designated by identical reference numerals, and detailed description thereof is omitted.
In FIG. 10, reference numeral 116 designates an A/D converter incorporated in the microcomputer 120. The A/D converter 116 converts the amplified output from the position sensor 114 into a digital signal. Reference numeral 111 designates an adder that calculates the difference between a value corresponding to the current position of the shift lens 119 and the target drive value for the shift lens 119. The output from the adder 111 provides an actual correction amount. Reference numeral 112 designates a low-pass filter (LPF) for reducing drive noise generated by an H bridge driver 113. The output from the LFP 112 is subjected to pulse width modulation (PWM) by the PWM section 117, followed by being delivered as the PWM output from the microcomputer 120. The shift lens 119 is driven by this PWM output via the H bridge driver 113.
The use of the PWM drive control method makes it possible to avoid internal loss, thereby improving energy conversion efficiency and hence reducing power consumption in contrast with the shake correcting device shown in FIG. 9.
Further, the use of the PWM drive control method makes it possible to turn off the drive current without using the power switches 804 and 805 appearing in FIG. 9, so that the peripheral arrangement associated with the power supply can be simplified. This point will be further described with reference to FIGS. 11A and 11B. FIG. 11A shows the arrangement of the input and output terminals of the H bridge driver 113 and elements associated therewith, and FIG. 11B shows the logic of the input and output terminals.
When the PWM drive control method is employed, outputs 1 and 2 from the H bridge driver 113 exhibit output values shown in FIG. 11B, according to the PWM waveform inputted to an input terminal 113a, and depending on the outputs 1 and 2, an electric current flows through a drive coil 113c to drive the shift lens 119.
An enable terminal 113b appearing in FIG. 11A, when its logic level is set to an L level, as shown in FIG. 11B, in the reproduction mode which does not need shake correction, brings the outputs 1 and 2 into a disabled (Hi-Z: high impedance) state to thereby make the state of power consumption equivalent to a power-off state. Therefore, through the execution of PWM drive, it is possible to turn off the drive current without using the power switches 804 and 805 in FIG. 9.
The above-described conventional shake correcting device based on the PWM drive control method using the H bridge circuit provides the advantageous effects of reduced power consumption and simplified construction as described above. However, it still suffers from the problem of impact noise generated by hitting of the shift lens 119 against the inner end of the lens barrel.
More specifically, when the PWM drive control method is employed, the controller is disposed in the microcomputer 120 as shown in FIG. 10, of such that the microcomputer 120 controls whether to enable the outputs from the H bridge driver 113. The power supply system is controlled such that power-system electric power (voltage of not lower than 5V) is supplied to the H bridge driver 113 alone, and control-system electric power (voltage e.g. of 3V) is supplied to the other component parts. When the shake correction is started immediately after the turning-on of the power of the image pickup apparatus or from a state e.g. in the reproduction mode, which does not need shake correction, the outputs from the H bridge driver 113 are switched from the disabled state to the enabled state, as described above, whereby the drive current is supplied to the drive coil 113c. 
However, the outputs from the H bridge driver 113 are enabled when the shift lens 119 is in the vicinity of the inner end of the lens barrel, so that while the output from the position sensor 114 assumes a value corresponding to a point close to the inner end of the lens barrel, the target drive value corresponds to a point close to the center position of the shift lens 119. For this reason, the PWM output to be applied to the H bridge driver 113 as the correction amount, which corresponds to the difference between the two values is such as will cause a sudden motion of the shift lens 119. Consequently, when the outputs from the H bridge driver 113 are enabled, a large electric current suddenly flows through the drive coil 113c of the shift lens 119. As a result, the shift lens 119 is caused to hit against the inner end of the lens barrel, which generates large impact noise.